U.S. patent number 5,460,640 [Application Number 07/931,075] was granted by the patent office on 1995-10-24 for alumina-rare earth oxide ceramic-metal bodies.
This patent grant is currently assigned to Valenite Inc.. Invention is credited to Sergej-Tomislav Buljan.
United States Patent |
5,460,640 |
Buljan |
* October 24, 1995 |
Alumina-rare earth oxide ceramic-metal bodies
Abstract
A fully dense ceramic-metal body including 40-88 v/o of an oxide
hard phase of, in v/o of the body, 4-88 v/o M-aluminum binary
oxides, where the binary oxide has a C-type rare earth, garnet,
.beta.-MAl.sub.11 O.sub.18, or perovskite crystal structure, and M
is a lanthanide or indium, and 0-79 v/o .alpha.-alumina; about
10-50 v/o of a hard refractory carbide, nitride, or boride as a
reinforcing phase; and about 2-10 v/o of a dispersed metal phase
combining Ni and Al mostly segregated at triple points of the
microstructure. The preferred metal phase contains a substantial
amount of the Ni.sub.3 Al ordered crystal structure. In the
preferred body, the reinforcing phase is silicon carbide partially
incorporated into the oxide grains, and bridges the grain
boundaries. The body including a segregated metal phase is produced
by densifying a mixture of the hard phase components and the metal
component, with the metal component being present in the starting
formulation as Ni powder and Al powder. The body may be used as a
cutting tool for machining nickel superalloys or cast iron at
speeds up to about 1000 sfm, feed rates up to about 0.012 in/rev,
and depth of cut up to about 0.10 inches.
Inventors: |
Buljan; Sergej-Tomislav (Acton,
MA) |
Assignee: |
Valenite Inc. (Madison Heights,
MI)
|
[*] Notice: |
The portion of the term of this patent
subsequent to June 8, 2010 has been disclaimed. |
Family
ID: |
27505024 |
Appl.
No.: |
07/931,075 |
Filed: |
August 17, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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914914 |
Jul 16, 1992 |
5279191 |
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693492 |
Apr 30, 1991 |
5216845 |
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701302 |
May 13, 1991 |
5271758 |
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595065 |
Oct 10, 1990 |
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Current U.S.
Class: |
75/233; 407/119;
419/10; 419/11; 419/12; 419/13; 419/14; 419/15; 419/16; 419/19;
419/20; 419/23; 419/24; 419/36; 419/38; 419/42; 419/48; 419/49;
75/235; 75/237; 75/238; 75/245; 75/249; 75/951; 82/1.11 |
Current CPC
Class: |
C04B
35/117 (20130101); C04B 35/645 (20130101); C04B
35/74 (20130101); C22C 29/12 (20130101); Y10T
82/10 (20150115); Y10T 407/27 (20150115); Y10S
75/951 (20130101) |
Current International
Class: |
C04B
35/111 (20060101); C04B 35/645 (20060101); C04B
35/71 (20060101); C04B 35/74 (20060101); C04B
35/117 (20060101); C22C 29/12 (20060101); C22C
29/00 (20060101); C22C 029/02 (); C22C 029/12 ();
C22C 029/18 (); B31B 001/00 (); B23B 001/00 () |
Field of
Search: |
;82/1.11,47
;51/281R,307,309 ;407/119 ;75/233,235,236,237,238,245,249,951
;419/10,11,12,13,14,15,16,19,20,23,24,36,38,42,48,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0062311 |
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Oct 1982 |
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EP |
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49127806 |
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Dec 1974 |
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JP |
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2071906 |
|
Mar 1990 |
|
JP |
|
Primary Examiner: Walsh; Donald P.
Assistant Examiner: Jenkins; Daniel
Attorney, Agent or Firm: Gregg; John W.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of commonly assigned,
U.S. Patent application Ser. No. 07/914,914, filed Jul. 16, 1992
now U.S. Pat. No. 5,279,191 by S.-T. Buljan, which is a
continuation-in-part of U.S. patent application Ser. Nos.
07/693/492, filed Apr. 30, 1991, now U.S. Pat. No. 5,216,845 and
07/701,302, filed May 13, 1991 now U.S. Pat. No. 5,271,758. Each
application Ser. Nos. 07/693,492 and of 07/701,302 is a
continuation-in-part of U.S. patent application Ser. No. 07/595,065
filed Oct. 10, 1990 and now abandoned. Application Ser. Nos.
07/595,065, 07/693,492, and 0/701,302 are incorporated herein by
reference.
Claims
I claim:
1. A ceramic-metal body having a density of at least about 95% of
theoretical density, said body comprising:
about 40-88 volume percent of an oxide hard phase consisting
essentially of, in volume percent based on the total volume of said
body, about 4-88 volume percent of at least one M-aluminum binary
oxide having a crystal structure selected from the group consisting
of C-type rare earth, garnet, .beta.-MAl.sub.11 O.sub.18, or
perovskite, wherein M is selected from the group consisting of
lanthanides and indium; 0 to about 79 volume percent of granular
.alpha.-alumina; and 0 to less than 5 volume percent of one or more
other oxides selected from the group consisting of magnesia,
zirconia, yttria, hafnia, and silica;
about 10-50 volume percent of a refractory reinforcing hard phase
consisting essentially of one or more materials selected from the
group consisting of carbides, nitrides, oxycarbides, and
oxynitrides of titanium, zirconium, hafnium, niobium, tantalum,
tungsten, and silicon; borides of titanium, tantalum, hafnium, and
tungsten; and combinations thereof; and
about 2-10 volume percent of a metal phase consisting essentially
of a combination of nickel and aluminum having a ratio of nickel to
aluminum of from about 70:30 to about 90:10 by weight and 0-5
weight percent of an additive selected from the group consisting of
titanium, zirconium, hafnium, vanadium, niobium, tantalcum,
chromium, molybdenum, tungsten, cobalt, boron, carbon, and
combinations thereof; wherein said metal phase is a non-continuous,
dispersed metal phase, and at least a major portion of said
non-continuous, dispersed metal phase is segregated at triple
points defined by grain surfaces of said hard phases.
2. A body in accordance with claim 1 wherein said reinforcing hard
phase comprises equiaxed particles in an amount of no more than 20
volume percent of said body, the remainder of said reinforcing hard
phase being platelets, elongated grains, or a combination
thereof.
3. A body in accordance with claim 1 wherein said at least one
M-aluminum binary oxide consists essentially of a combination of a
lanthanide-aluminum binary oxide having a rare earth perovskite
crystal structure and a lanthanide-aluminum binary oxide having a
.beta.-NaAl.sub.11 O.sub.17 crystal structure.
4. A body in accordance with claim 1 wherein the composition, in
volume percent, of said body is bounded by and contained within the
three-dimensional solid defined by points a, b, c, d, e, f, g, and
h of FIG. 3.
5. A body in accordance with claim 4 wherein said at least one
M-aluminum binary oxide consists essentially of (In,Al).sub.2
O.sub.3 having a C-type rare earth crystal structure.
6. A body in accordance with claim 5 wherein said reinforcing hard
phase consists essentially of silicon carbide, and said body
comprises:
about 45-68 volume percent of said oxide hard phase consisting
essentially of, in volume percent based on the total volume of said
body, about 4.5-68 volume percent of said (In,Al).sub.2 O.sub.3 ; 0
to about 61 volume percent of said alumina; and 0 to less than 5
volume percent of said one or more other oxides;
about 30-50 volume percent of said silicon carbide; and
about 2-5 volume percent of said metal phase.
7. A body in accordance with claim 4 wherein said at least one
M-aluminum binary oxide consists essentially of a combination of
LnAl.sub.3 O.sub.9 having a rare earth perovskite crystal structure
and LnAl.sub.3 O.sub.9 having a .beta.-NaAl.sub.11 O.sub.17 crystal
structure, wherein Ln is a lanthanide.
8. A body in accordance with claim 7 wherein said reinforcing hard
phase consists essentially of silicon carbide, and said body
comprises:
about 45-73 volume percent of said oxide hard phase consisting
essentially of, in volume percent based on the total volume of said
body, 0 to about 73 volume percent of said LnAlO.sub.3 ; 0 to about
73 volume percent of said LnAl.sub.3 O.sub.9 ; 0 to about 40.5
volume percent of said alumina; and 0 to less than 5 volume percent
of said one or more other oxides;
about 25-50 volume percent of said silicon carbide; and
about 2-5 volume percent of said metal phase.
9. A body in accordance with claim 1 wherein said at least one
M-aluminum binary oxide consists essentially of Ln.sub.3 Al.sub.5
O.sub.12 having a rare earth garnet crystal structure; Ln is a
lanthanide; and the composition, in volume percent, of said body is
bounded by and contained within the three-dimensional solid defined
by points i, b, c, j, k, f, g, and l of FIG. 3.
10. A body in accordance with claim 9 wherein said reinforcing hard
phase consists essentially of silicon carbide, and said body
comprises:
about 45-68 volume percent of said oxide hard phase consisting
essentially of, in volume percent based on the total volume of said
body, about 10-68 volume percent of said Ln.sub.3 Al.sub.5 O.sub.12
; 0 to about 48 volume percent of said alumina; and 0 to less than
5 volume percent of said one or more other oxides;
about 30-50 volume percent of said silicon carbide; and
about 2-5 volume percent of said metal phase.
11. A body in accordance with claim 1 wherein said reinforcing hard
phase is present in the form of platelets or elongated grains.
12. A body in accordance with claim 11, wherein at least a portion
of said reinforcing hard phase is present as silicon carbide, and
at least a portion of said silicon carbide is partially
incorporated into grains of said oxide phase and bridges the grain
boundaries of the microstructure of said body.
13. A body in accordance with claim 11 wherein said reinforcing
hard phase is present in the form of single crystal whiskers having
an average aspect ratio of length to diameter between 3:1 and 10:1
or in the form of platelets having an average ratio of length to
width to thickness between about 3:2:1 and about 10:10:1.
14. A body in accordance with claim 1 wherein said metal phase
comprises a combination of a Ni.sub.3 Al ordered crystal structure,
or a Ni.sub.3 Al ordered crystal structure coexistent with or
modified by said additive, and one or more nickel-aluminum
alloys.
15. A body in accordance with claim 1 wherein said body is coated
with one or more adherent, compositionally distinct layers, each
layer being a material or solid solution of materials selected from
the group consisting of carbides, nitrides, and carbonitrides of
titanium, zirconium, hafnium, vanadium niobium tantalum, chromium,
and molybdenum, oxides of aluminum and zirconium, and diamond.
16. A method for machining a workpiece comprising the steps of:
turning said workpiece on a lathe at an effective cutting speed of
up to about 1000 surface feet per minute;
moving a ceramic-metal cutting tool across the face of said
workpiece at a feed rate of up to about 0,012 inches per
revolution; and
cutting said workpiece with said ceramic-metal cutting tool to
effect a depth of cut of up to about 0.10 inches per pass;
wherein said ceramic-metal cutting tool has a density of at least
about 95% of theoretical, and comprises:
about 40-88 volume percent of an oxide hard phase consisting
essentially of, in volume percent based on the total volume of said
cutting tool, about 4-88 volume percent of at least one M-aluminum
binary oxide having a crystal structure selected from the group
consisting of C-type rare earth, garnet, .beta.-MAl.sub.11
O.sub.18, or perovskite, wherein M is selected from the group
consisting of lanthanides and indium; 0 to about 79 volume percent
of granular .alpha.-alumina; and 0 to less than 5 volume percent of
one or more other oxides selected from the group consisting of
magnesia, zirconia, yttria, hafnia, and silica;
about 10-50 volume percent of a refractory reinforcing hard phase
consisting essentially of one or more materials selected from the
group consisting of carbides, nitrides, oxycarbides, and
oxynitrides of titanium, zirconium, hafnium, niobium, tantalum,
tungsten, and silicon; borides of titanium, tantalum, hafnium, and
tungsten; and combinations thereof; and
about 2-10 volume percent of a metal phase consisting essentially
of a combination of nickel and aluminum having a ratio of nickel to
aluminum of from about 70:30 to about 90:10 by weight and 0-5
weight percent of an additive selected from the group consisting of
titanium, zirconium, hafnium, vanadium, niobium, tantalum,
chromium, molybdenum, tungsten, cobalt, boron, carbon, and
combinations thereof; wherein said metal phase is a non-continuous,
dispersed metal phase, and at least a major portion of said
non-continuous, dispersed metal phase is segregated at triple
points defined by grain surfaces of said hard phases.
17. A method in accordance with claim 16 wherein said metal phase
comprises a combination of a Ni.sub.3 Al ordered crystal structure,
or a Ni.sub.3 Al ordered crystal structure coexistent with or
modified by said additive, and one or more nickel-aluminum
alloys.
18. A method in accordance with claim 16 wherein said cutting tool
is coated with one or more adherent, compositionally distinct
layers, each layer being a material or solid solution of materials
selected from the group consisting of carbides, nitrides, and
carbonitrides of titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, and molybdenum, oxides of aluminum and
zirconium, and diamond.
19. A method for the preparation of a ceramic-metal body comprising
the steps of:
preparing a mixture comprising (a) about 40-88 volume percent of
hard refractory oxide components consisting essentially of, in
volume percent based on the total volume of said body, about 4-88
of at least one M-aluminum binary oxide having a crystal structure
selected from the group consisting of C-type rare earth, garnet,
.beta.-MAl.sub.11 O.sub.18, or perovskite, wherein M is selected
from the group consisting of lanthanides and indium; 0 to about 79
volume percent of granular .alpha.-alumina; and 0 to less than 5 of
one or more other oxides selected from the group consisting of
magnesia, zirconia, yttria, hafnia, and silica; (b) about 10-50
volume percent of one or more hard refractory reinforcing
components selected from the group consisting of carbides,
nitrides, oxycarbides, and oxynitrides of titanium, zirconium,
hafnium, niobium, tantalum, tungsten, and silicon; borides of
titanium, tantalum, hafnium, and tungsten; and combinations
thereof; and (c) about 2-10 volume percent of a metal component
consisting essentially of a combination of nickel powder and
aluminum powder having a ratio of nickel powder to aluminum powder
of from about 70:30 to about 90:10 by weight and 0-5 weight percent
of an additive selected from the group consisting of titanium,
zirconium, hafnium, vanadium, niobium, tantalum, chromium,
molybdenum, tungsten, cobalt, boron, carbon, and combinations
thereof; and
densifying said mixture to form a ceramic metal body having a
density of at least 95% of theoretical density and having a
granular microstructure within which said metal component forms a
non-continuous, dispersed metal phase, at least a major portion of
said non-continuous, dispersed metal phase being segregated at
triple points defined by grain surfaces of said granular
microstructure.
20. A method in accordance with claim 19 wherein said reinforcing
components comprise equiaxed particles in an amount of no more than
20 volume percent of said body, the remainder of said reinforcing
components being platelets, elongated grains, or a combination
thereof.
21. A method in accordance with claim 19 wherein said densifying
step comprises densifying said mixture by sintering, continuous
cycle sinterhiping, two step sintering-plus-HIPing, hot pressing,
or hot isostatic pressing to form said body.
22. A method in accordance with claim 19 wherein said densifying
step comprises the sub-steps of:
adding an organic binder to said mixture to form a slurry;
drying said slurry to remove said binder and form a dried
powder;
pressing said dried powder to form a green compact; and
densifying said green compact by hot isostatic pressing.
23. A method in accordance with claim 19 wherein said reinforcing
hard phase comprises silicon carbide platelets or elongated grains;
and during said densifying step at least a portion of said silicon
carbide platelets or elongated grains is partially incorporated
into grains of said oxide component and bridges the grain
boundaries of said granular microstructure.
Description
This application is also related to commonly assigned U.S. patent
application Ser. Nos. 07/576,241, filed Aug. 31, 1990 and now
abandoned; 07/632,237 and 07/632,238, both filed Dec. 20 1990 now
U.S. Pat. Nos. 5,053,074 and 5,089,047 respectively; and
07/635,408, filed Dec. 21, 1990 now U.S. Pat. No. 5,841,261.
BACKGROUND OF THE INVENTION
This invention relates to oxide ceramic bodies for use as cutting
tools, wear parts, and the like. The bodies contain at least one
indium/aluminum or rare earth/aluminum binary oxide optionally
mixed with .alpha.-alumina, a reinforcing phase, and a dispersed
metal phase. In particular the invention relates to such bodies
containing a metal phase including both nickel and aluminum. The
invention also involves methods for preparation and use of such
bodies.
Ceramic-metal or cermet tools for steel machining have greatly
improved the productivity and efficiency of the metal removal
process. The performance of a number of cermet materials, which
principally are based on refractory metal carbides or nitrides
bonded with cobalt, nickel, molybdenum, or alloy binders,
inherently is limited by the chemical interaction between the hard
phase and steel workpiece materials. This becomes particularly
evident as increased cutting speeds generate more heat, increasing
the chemical reactivity of both the tool material and the
workpiece. Such chemical reactions between the cutting tool and
steel workpiece accelerate wear and reduce crater resistance of the
tool.
Attempts have been made to utilize alumina ceramics and
alumina-based composites such as alumina-titanium carbide
composites for use as cutting tools for steel machining. The
broader use of this class of materials, however, has been
restricted by their inherent brittleness.
Of particular concern has been the need for cutting tools suitable
for machining of high nickel superalloys. The high temperature
nickel based superalloys, for example Inconel.RTM. alloys
(available from Huntington Alloys, Inc., Huntington, W. Va.),
present the advantages of deformation resistance and retention of
high strength over a broad range of temperatures. Because of their
high strength at elevated temperatures, however, these alloys are
much more difficult to machine than steels.
Ceramic-metal (cermet) tools, for the most part, have shown only
limited effectiveness in machining of nickel based alloys. These
cermet materials are based principally on refractory metal carbides
or nitrides bonded with cobalt, nickel, molybdenum, or alloy
binders. Commercially available cutting tools, for example cobalt
cemented tungsten carbide, can be utilized for such machining only
at relatively low cutting speeds and hence provide low
productivity.
Attempts have been made to utilize alumina ceramics and
alumina-based composites such as alumina-titanium carbide
composites for use as cutting tools for high temperature nickel
based superalloy machining. The use of this class of materials,
however, has been restricted by their inherently low fracture
toughness, limiting the usable feed rate and depth of cut.
Alumina-silicon carbide whisker composites have provided some
increase in fracture toughness, but the whisker component, due to
its fibrous nature, requires extremely careful handling to assure
safety.
Accordingly, it would be of great value to find a cutting tool
suitable for machining difficult-to-work metals such as high
temperature nickel based superalloys using a cutting tool body
which exhibits improved chemical wear resistance and performance
when compared to conventional ceramic metal-cutting tool materials,
improved fracture toughness compared to known alumina-titanium
carbide composites, and improved ease of fabrication compared to
known alumina-silicon carbide whisker composite materials. The body
described herein is directed to achieving such a cutting tool.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a ceramic-metal body having
a density of at least about 95% of theoretical density. The body
includes about 40-88 volume percent (v/o) of an oxide hard phase
consisting essentially of, in v/o based on the total volume of the
body, about 4-88 v/o of at least one M-aluminum binary oxide having
a crystal structure selected from the group consisting of C-type
rare earth, garnet, .beta.-MAl.sub.11 O.sub.18, or perovskite; 0 to
about 79 volume percent of granular .alpha.-alumina; and 0 to less
than 5 volume percent of one or more other oxides selected from the
group consisting of magnesia, zirconia, yttria, hafnia, and silica.
M is a lanthanide or indium. The body also includes about 10-50 v/o
of a refractory reinforcing hard phase consisting essentially of
one or more materials selected from the carbides, nitrides,
oxycarbides, and oxynitrides of titanium, zirconium, hafnium,
niobium, tantalum, tungsten, and silicon; borides of titanium,
tantalum, hafnium, and tungsten; and combinations thereof. The body
further includes about 2-10 v/o of a metal phase consisting
essentially of a combination of nickel and aluminum having a ratio
of nickel to aluminum of from about 70:30 to about 90:10 by weight
and 0-5 weight percent (w/o) of an additive selected from titanium,
zirconium, hafnium, vanadium, niobium, tantalum, chromium,
molybdenum, tungsten, cobalt, boron, carbon, and combinations
thereof. The metal phase is a non-continuous, dispersed metal
phase, and at least a major portion of the non-continuous,
dispersed metal phase is segregated at triple points defined by
grain surfaces of the hard phases.
In a narrower aspect of the invention, equiaxed particles are
included in the reinforcing hard phase in an amount of no more than
20 v/o of the body, the remainder of the reinforcing hard phase
being platelets, elongated grains, or a combination thereof.
In another narrower aspect of the invention, the body includes
silicon carbide in the form of platelets or elongated grains as the
reinforcing hard phase, and at least a portion of the silicon
carbide is partially incorporated into grains of the oxide phase
and bridges the grain boundaries of the microstructure of the
body.
In another aspect, the invention is a method for machining a
workpiece involving the steps of turning the workpiece on a lathe
at an effective cutting speed of up to about 1000 surface feet per
minute, moving a ceramic-metal cutting tool across the face of the
workpiece at a feed rate of up to about 0.012 inches per
revolution, and cutting the workpiece with the ceramic-metal
cutting tool to effect a depth of cut of up to about 0.10 inches
per pass. The ceramic-metal cutting tool has a density of at least
about 95% of theoretical. The tool includes about 40-88 v/o of an
oxide hard phase consisting essentially of, in v/o based on the
total volume of the cutting tool, about 4-88 v/o of at least one
M-aluminum binary oxide having a crystal structure selected from
the group consisting of C-type rare earth, garnet,
.beta.-MAl.sub.11 O.sub.18, or perovskite; 0 to about 79 volume
percent of granular .alpha.-alumina; and 0 to less than 5 volume
percent of one or more other oxides selected from the group
consisting of magnesia, zirconia, yttria, hafnia, and silica. M is
a lanthanide or indium. The tool also includes about 10-50 v/o of a
refractory reinforcing hard phase consisting essentially of one or
more materials selected from the carbides, nitrides, oxycarbides,
and oxynitrides of titanium, zirconium, hafnium, niobium, tantalum,
tungsten, and silicon; borides of titanium, tantalum, hafnium, and
tungsten; and combinations thereof. The tool further includes about
2-10 v/o of a metal phase consisting essentially of a combination
of nickel and aluminum and 0-5 weight percent (w/o) of an additive
selected from titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, molybdenum, tungsten, cobalt, boron, carbon,
and combinations thereof. The ratio of nickel to aluminum is about
70:30 to about 90:10 by weight. The metal phase is a
non-continuous, dispersed metal phase, and at least a major portion
of the non-continuous, dispersed metal phase is segregated at
triple points defined by grain surfaces of the hard phases.
In yet another aspect, the invention is a method for the
preparation of a ceramic-metal body. The method includes preparing
a mixture including about 40-88 volume percent of hard refractory
oxide components consisting essentially of, in volume percent based
on the total volume of the body, about 4-88 of at least one
M-aluminum binary oxide having a crystal structure selected from
C-type rare earth, garnet, .beta.-MAl.sub.11 O.sub.18, or
perovskite; 0 to about 79 volume percent of granular
.alpha.-alumina; and 0 to less than 5 of one or more other oxides
selected from the group consisting of magnesia, zirconia, yttria,
hafnia, and silica. M is selected from the group consisting of
lanthanides and indium. The mixture also includes about 10-50
volume percent of one or more hard refractory reinforcing
components selected from the carbides, nitrides, oxycarbides, and
oxynitrides of titanium, zirconium, hafnium, niobium, tantalum,
tungsten, and silicon; borides of titanium, tantalum, hafnium, and
tungsten; and combinations thereof. The mixture further includes
about 2-10 v/o of a metal component consisting essentially of a
combination of nickel powder and aluminum powder having a ratio of
nickel powder to aluminum powder of from about 70:30 to about 90:10
by weight and 0-5 w/o of an additive selected from titanium,
zirconium, hafnium, vanadium, niobium, tantalum, chromium,
molybdenum, tungsten, cobalt, boron, carbon, and combinations
thereof. The method further includes the step of densifying the
mixture to form a ceramic metal body having a density of at least
95% of theoretical density and having a granular microstructure
within which the metal component forms a non-continuous, dispersed
metal phase. At least a major portion of the non-continuous,
dispersed metal phase is segregated at triple points defined by
grain surfaces of the granular microstructure.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, together with
other objects, advantages and capabilities thereof, reference is
made to the following Description and appended Claims, together
with the Drawings, in which:
FIGS. 1 and 2 are schematic illustrations in cross-section of the
microstructure of the material of bodies in accordance with
different embodiments of the invention, illustrating the
segregation of the metal phase at the triple points and
incorporation of a portion of the reinforcing hard phase into oxide
phase grains. In FIG. 1, the reinforcing hard phase is a whisker
phase, while in FIG. 2 it is a platelet phase.
FIG. 3 is a quarternary diagram graphically depicting the
proportions of the phases present in bodies in accordance with
different embodiments of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The fully dense ceramic materials described herein include at least
two hard phases, one or more oxide hard phases and an additional,
reinforcing hard phase of equiaxed or elongated grains of one or
more refractory carbides, nitrides, oxycarbides, oxynitrides,
borides or combinations of these.
The oxide component is present in the material in an amount of
about 40-88 v/o. This component includes at least one binary oxide
containing aluminum, indium or a lanthanide, and oxygen. Examples
of such binary oxides are (In,Al).sub.2 O.sub.3, which contains no
rare earth element but has a C-type rare earth crystal structure;
Ln.sub.3 Al.sub.5 O.sub.12, with a rare earth garnet structure;
LnAlO.sub.3, with a perovskite structure; and LnAl.sub.11 O.sub.18,
with a .beta.-alumina structure. Typically, the LnAlO.sub.3 and
LnAl.sub.11 O.sub.18 are combined to make up the rare earth oxide
portion of the binary oxide component, as described below. As used
herein, the term "Ln" refers to the lanthanide series rare earth
elements and includes, for example, neodymium, samarium,
dysprosium, erbium, and solid solutions thereof. Also as used
herein, the terms ".beta.-alumina structure" "NaAl.sub.11 O.sub.17
structure", and the like refer to a material isostructural with
NaAl.sub.11 O.sub.17, a material commonly referred to in the art by
the idealized formula ".beta.-NaAl.sub.11 O.sub.17 " or by the term
".beta.-alumina". This material originally was thought to be
.beta.-alumina, but subsequently was found not to be a pure
alumina. The material and its crystal structure are described in
more detail by G.E. Rankin et al. (J. Amer. Cer. Soc. 38, 568
(1916)) and W. C. Bragg et al. (Krystallogr. 77, 255 (1931)). Both
the Rankin et al. and the Bragg et al. papers are incorporated
herein by reference.
Optionally, the oxide component also includes .alpha.-alumina. As
used herein, the term ".alpha.-alumina" is intended to mean
aluminum oxide having a nominal formula Al.sub.2 O.sub.3, which is
substantially completely of the trigonal (carborundum) crystal
structure, and which may (or may not) be further modified by or
coexist with small amounts, i.e. less than 5 v/o, of magnesia,
zirconia, yttria, hafnia, and/or silica. An example of such an
addition is the addition of a small amount of MgO as a grain growth
inhibiting agent. Preferably, for example in a cutting tool body,
the content of silica is no more than about 2 v/o; and that of
other impurities, no more than about 1 v/o. The additional,
reinforcing hard phase is present in an effective amount of about
10-50 v/o, depending on the toughness and chemical resistance
desired for the ceramic-metal body. Typically, the reinforcing hard
phase is silicon carbide in an amount of about 30-50 v/o.
Alternatively, the reinforcing hard phase may be a hard refractory
carbide, nitride, oxycarbide, oxynitride, or boride of titanium,
zirconium, hafnium, niobium, tantalum, tungsten, boron, silicon, or
mixtures or solid solutions of these in an amount of about 10-50
v/o. Within that range, lowering the carbide content, if any, in
the second phase decreases the chemical solubility of, for example,
a cutting tool material with respect to ferrous alloys. Reinforcing
phase carbide additions at the higher end of this range increase
the toughness of the material, increasing impact and wear
resistance in applications such as milling. Thus the properties of
the material may, to some extent, be preselected by balancing the
reinforcing hard phase components. Examples of suitable materials
for the reinforcing hard phase are silicon carbide, titanium
carbide, titanium nitride, hafnium carbide, hafnium nitride,
tantalum carbide, tantalum nitride, tungsten carbide, boron
carbide, titanium diboride, or combinations thereof.
The reinforcing hard phase may include equiaxed or nearly equiaxed
grains of about 1 .mu.m average diameter and/or acicular grains,
for example whiskers, fibers, or platelets. The acicular grains may
be elongated grains with an aspect ratio of about 3:1 to 10:1,
length to diameter, and may be polycrystalline fibers or single
crystal whiskers. Alternatively, the acicular grains may be in the
form of single crystal platelets. The ratio of length to width to
thickness of such platelets is preferably about 3:2:1 to 10:10:1.
When combined with acicular dispersoid grains, the content of
equiaxed grain reinforcing component preferably should be limited
to no more than about 20 v/o of the body, to maximize the fracture
strength of the body. The term "equiaxed", as used herein, refers
to grains of spherical or near-spherical geometry, that is having
an aspect ratio of 1:1 to 1.5:1, length to diameter.
In the preferred microstructure, any silicon carbide in the form of
whiskers, fibers, or platelets is at least partially incorporated
into the oxide phase grains during the densification process,
linking these grains together across the grain boundaries. This
linking is shown schematically in FIGS. 1 and 2, and is described
further below. Incorporating platelets as a major part or all of
the reinforcing hard phase presents the added advantage of
simplifying the fabrication of the ceramic-metal bodies by
lessening the need for added safety measures required when working
with ceramic whisker or fiber components.
The hard phases coexist in the microstructure of the body with an
intermetallic phase combining nickel and aluminum, in an amount of
about 2-10 v/o of the starting formulation. It is essential for
optimization of this material, for example for use as a cutting
tool, that this metal phase include both nickel and aluminum. The
metal powders added to the starting formulation include nickel in
an amount of about 70-90 w/o, and aluminum in an amount of about
10-30 w/o, both relative to the total weight of the metal powder.
Since nickel does not readily wet alumina, the addition of aluminum
to the metal phase in an amount of less than about 10 w/o can
result in a material of inferior properties. The material becomes
more difficult to sinter, and the dispersion of the nickel in such
a material is poor. Conversely, the addition of aluminum in an
amount greater than about 30 w/o of the metal phase can lower the
hardness and chemical stability of the material, also resulting in
inferior properties. A minor amount of titanium, zirconium,
hafnium, vanadium, niobium, tantalum, chromium, molybdenum,
tungsten, cobalt, boron, and/or carbon, the total amount not to
exceed about 5 w/o of the metal phase, may also be included.
The preferred composition is 12-14 w/o Al, balance Ni. In the most
preferred compositions the Ni:Al ratio results in the formation of
a substantially Ni.sub.3 Al metal phase, having the Ni.sub.3 Al
ordered crystal structure. The Ni.sub.3 Al ordered crystal
structure may be substantially completely of the true Ni.sub.3 Al
phase, or this true Ni.sub.3 Al phase may be only partially
developed and exist in combination with one or more nickel-aluminum
alloys. The Ni.sub.3 Al ordered crystal structure preferably is
present in an amount of at least about 40 v/o, typically about
40-80 v/o, of the metal phase. In some compositions, this ordered
crystal structure may coexist with or be modified by the
abovementioned additives. Thus, as used herein, the term "metal
phase" does not necessarily denote a single phase, but may indicate
a polyphase component of the microstructure of the body.
The best combination of properties (hardness and fracture
toughness) for the articles described herein, particularly for
cutting tool applications, is obtained when total metal addition is
in the most preferred range of about 4-10 v/o. The beneficial
effect of the low amounts described herein for the intermetallic
phase is particularly unexpected, since at such lower amounts this
phase is less likely to be acting as a continuous binder for the
hard phases in a manner similar to known cermets, for example
tungsten carbide/cobalt materials or nickel-molybdenum bonded
carbides.
A preferred microstructure for the ceramic-metal articles described
herein is schematically illustrated in FIGS. 1 and 2. FIG. 1 shows
ceramic-metal material 10, including grains 12 of a hard binary
oxide, alumina grains 14, silicon carbide reinforcing hard phase
whiskers 16, and metal phase 18. Grains 12 and 14 make up the oxide
phase, while grains 12 and 14 and whiskers 16 are the hard phases.
Metal phase 18 is dispersed, non-continuous, and substantially
segregated at "triple points" of the material, i.e. at points where
the surfaces of at least three grains come together or would
contact one another if the metallic phase were not present in the
fully dense material. FIG. 1 shows metal phase 18 as segregates 20
disposed at triple points 22 between hard phase grains 12, 14,
and/or 16. These finely divided segregates are made up of a
combination of Ni--Al alloys with the intermetallic Ni.sub.3 Al
compound.
The segregation is effected by adding nickel and aluminum to the
above described hard phase materials as nickel and aluminum powders
rather than as the prereacted Ni.sub.3 Al compound. Since nickel
and nickel-rich Ni--Al alloys wet alumina poorly, the metal phase
tends to segregate at the triple points, as described above.
FIG. 1 also shows a microstructure in which a significant portion
of silicon carbide whiskers 16, preferably about 5-50 v/o and most
preferably at least about 10 v/o, have one or both ends
incorporated into oxide phase grains 12 and 14, rather than being a
completely intergranular phase. Such incorporation has been
observed only between silicon carbide reinforcing phase and the
oxide grains. This incorporation toughens the incorporating grains
at the microscopic scale. It also bridges the boundaries between
grains, increasing the fracture toughness of the body on a
microscopic scale. The composite bodies exhibiting a microstructure
of both incorporated reinforcing hard phase and segregated metal
phase exhibit unexpectedly high strength; that is a modulus of
rupture as much as 50-100% higher than that of conventional
composites of alumina and silicon carbide whiskers alone is
observed.
FIG. 2 illustrates a microstructure similar to that shown in FIG. 1
in which like features are indicated by the same reference
numerals. However, substituted for silicon carbide whiskers 16 of
FIG. 1 are silicon carbide platelets 24 in FIG. 2. One or more
edges or corners of platelets 24 are incorporated into oxide phase
grains 12 and 14, imparting increased fracture toughness and
strength similar to that described for the material of FIG. 1.
Preferably about 5-50 v/o, and most preferably at least about 10
v/o of the platelets are so incorporated.
The above-described hard, fracture-resistant body is achieved only
when the above-described binary oxide, reinforcing phase, metal
phase, and optionally alumina are present in the ranges specified
above. The preferred ranges are shown graphically in FIG. 3, with
the approximate composition, in volume percent, of the body
described herein bounded by and contained within the
three-dimensional solid defined by points a, b, c, d, e, f, g, and
h of FIG. 3. The volume percents of binary oxide, alumina,
reinforcing phase, and metal phase represented by points a, b, c,
d, e, f, g, and h are shown in Table I.
The most preferred ranges for a body in which the binary oxide is
(a) (In,Al).sub.2 O.sub.3 having a C-type rare earth crystal
structure, or (b) one or both of a rare earth perovskite
LnAlO.sub.3 and a rare earth hexagonal .beta.-LnAl.sub.11 O.sub.18
are the same as that described above for the body in general; thus
the approximate most preferred composition, in volume percent, of
these bodies is bounded by and contained within the same
three-dimensional solid defined by points a, b, c, d, e, f, g, and
h of FIG. 3. Where the reinforcing hard phase of such a body is
silicon carbide, the most preferred ranges are narrower. For the
(In,Al).sub.2 O.sub.3 containing body, the preferred ranges are
approximately: total oxide phase, 45-68 v/o; (In,Al).sub.2 O.sub.3
C-type rare earth structure, 4.5-68 v/o; alumina, 0-63.5 v/o; SiC,
30-50 v/o; metal, 2-5 v/o. For the body containing
perovskite/.beta.-alumina and silicon carbide reinforcing hard
phase, the preferred ranges are approximately: total oxide phase,
45-73 v/o; LnAlO.sub.3 rare earth perovskite structure, 0-73 v/o;
LaAl.sub.11 O.sub.18 .beta.-alumina structure, 0-73 v/o; alumina,
0-40.5 v/o; SiC, 25-50 v/o; metal, 2-5 v/o.
The most preferred ranges for a body in which the binary oxide is a
rare earth garnet with a nominal formula Ln.sub.3 Al.sub.5 O.sub.12
are also shown graphically in FIG. 3, with the approximate most
preferred composition, in volume percent, of the body bounded by
and contained within the three-dimensional solid defined by points
i, b, c, j, k, f, g, and 1 of FIG. 3. The approximate volume
percents of binary oxide, alumina, reinforcing phase, and metal
phase represented by points i, b, c, j, k, f, g, and 1 are shown in
Table I. Where the reinforcing hard phase is silicon carbide, the
most preferred ranges are narrower, approximately: total oxide
phase, 45-68 v/o; Ln.sub.3 Al.sub.5 O.sub.12 rare earth garnet,
10-68 v/o and most preferably 10-30 v/o; alumina, 0-48 v/o; SiC,
30-50 v/o; metal, 2-5 v/o.
TABLE I ______________________________________ refrnce. ltr.: a b c
d e f ______________________________________ binary oxide: 80 40 4
8 88 48 alumina: 0 0 36 72 0 0 reinf. phase: 10 50 50 10 10 50
metal phase: 10 10 10 10 2 2 ______________________________________
refrnce. ltr.: g h i j k l ______________________________________
binary oxide: 4.8 8.8 70 7 78 7.8 alumina: 43.2 79.2 0 63 0 70.2
reinf. phase: 50 10 20 20 20 20 metal phare: 2 2 10 10 2 2
______________________________________
The preferred average grain size (equivalent diameter, that is the
diameter of a sphere of equal volume to the average grain) of the
equiaxed phase grains, that is the oxide phase and equiaxed
reinforcing phase, in a densified body of this material for cutting
tool use is about 0.1-5 .mu.m; the most preferred, 1.5-2 .mu.m. In
other articles for applications where strength requirements are
lower, e.g. sand blasting nozzles, a larger grain size for the
equiaxed phases, e.g. about 5-20 .mu.m, may prove satisfactory. For
elongated grain components, the preferred sizes are about 0.5-1.0
.mu.m fiber or whisker diameter and an aspect ratio of 3:1 to 10:1
(length to diameter). For platelet components, about 0.5-1.0 .mu.m
platelet thickness, and a ratio of length to width to thickness of
about 3:2:1 to 10:10:1 is preferred.
A typical method for preparation of the bodies described herein
involves several steps. In order to obtain a dense ceramic body a
mixture of the oxide powders in the desired volume ratio is dry
ball milled for 24 hours using alumina milling media, and screened
through 80 mesh screen. This base composition is then combined with
the reinforcing phase powder, whiskers, fibers, and/or platelets at
the desired volume ratios by forming a suspension of the components
in methanol. The resulting slurry is then sonicated to disperse any
agglomerates, mixed for 5 minutes using a high shear mixer, and pan
dried at 65.degree. C. for 16 hours. The dried powder is dry ball
milled for 2 hours using polyethylene media and screened through 60
mesh screen.
The mixture then may be densified by methods known to be suitable
for alumina-based materials, for example sintering, continuous
cycle sintar-plus-HIP, two step sintar-plus-HIP, hot pressing, or
hot isostatic pressing, all known in the art. (HIP=hot isostatic
pressing.) However, it is important that the nickel and aluminum of
the metal phase be added to the mixture to be densified as nickel
and aluminum powders rather than as prereacted nickel aluminide, in
order to achieve during densification the segregation of the metal
phase at the triple points of the microstructure, as described
above. For example, the above-described mixture may be hot pressed
at a temperature of about 1650.degree.-1850.degree. C. to obtain a
dense body. Alternatively, a green compact may be prepared by
adding an organic binder to the powder mixture to form a slurry,
subsequently removing the binder by drying the slurry to form a
dried powder, and pressing the dried powder to form the green
compact. The green compact is then densified by hot isostatic
pressing.
For certain applications such as cutting tools the articles
described herein may be coated with refractory materials to provide
certain desired surface characteristics. The preferred coatings
have one or more adherent, compositionally distinct layers of
refractory metal carbides and/or nitrides, e.g. of titanium,
tantalum, or hafnium, and/or oxides, e.g. of aluminum or zirconium,
or combinations of these materials as different layers and/or solid
solutions. Especially preferred for the oxide based material is an
alumina coating, because of its inherent compatibility with its
substrate, or a chemical vapor deposited (CVD) diamond coating,
because of its exceptional hardness. Both alumina and diamond
coatings provide exceptional chemical stability, wear resistance,
and high hardness at high temperatures.
When shaped as cutting tools, the bodies described herein may be
used for machining of high temperature nickel-based alloys,
including those known in the art as superalloys. The following
description of the method is directed to an exemplary Inconel
alloy, Inconel 718, but is also applicable to other high
temperature nickel based, iron based, and cobalt based superalloys
as well as to other materials, including difficult-to-work
materials. As used herein, the term "difficult-to-work" is intended
to refer to the machining characteristics of workpiece materials
which are significantly more difficult to work than typical steel
workpieces, necessitating slow machining speeds, slow feed rates,
and/or shallow depth of cut when machined using conventional
tungsten carbide-cobalt cutting tools. Such difficult-to-work
materials include high temperature nickel based metal alloys,
including the type known in the art as superalloys, as well as
other difficult-to-work alloys based on iron and cobalt.
The typical turning or milling speed for such high temperature
nickel based materials ranges from as low as 5-20 sfm (surface feet
per minute), for milling Inconel superalloys with high speed steel
tools, to as high as 30-100 sfm, for turning Inconel superalloys
with carbide tools (Materials Engineering Materials Selector 90,
C88 (1979)), typically tungsten carbide-cobalt tools. Utilization
of the above-described ceramic-metal tools, however, permits an
unexpectedly large increase in the machining speed, e.g. on the
order of one or two orders of magnitude.
In carrying out the method described herein, a bar of Inconel alloy
may be turned on a lathe using an alumina ceramic-metal cutting
tool as described above. An effective turning speed of up to about
1000 sfm, a feed rate of up to about 0.012 in/rev, and a depth of
cut of up to about 0.10 inches may be tolerated by these cutting
tools. Alternatively, the method may involve milling, drilling,
tapping, reaming, broaching, grooving, threading, or other
machining operation using a cutting tool material as described
herein. Also alternatively, the workpiece may be another material,
including those which are similarly difficult to machine.
The following Examples are presented to enable those skilled in the
art to more clearly understand and practice the present invention.
These Examples should not be considered as a limitation upon the
scope of the present invention, but merely as being illustrative
and representative thereof.
EXAMPLE 1
Ceramic-metal bodies were prepared from a powder mixture of 8 v/o
metal (86.7 w/o nickel, 13.3 w/o aluminum, each as a powder,
approximately corresponding to a Ni.sub.3 Al stoichiometric ratio),
27.6 v/o equiaxed solid solution tungsten titanium carbide powder
(nominal formula (W.sub.0.5 Ti.sub.0.5)C), and a mixture of erbium
oxide and aluminum oxide powders in an amount to yield 38.6 v/o of
.beta.-ErAl.sub.11 O.sub.19 and 25.8 v/o .alpha.-alumina, as
follows:
The oxides, tungsten titanium carbide, nickel, and aluminum powders
in the desired ratio were milled in a 500 cc capacity tungsten
carbide attritor mill using cemented carbide (WC-Co) milling media
for 2 hr at 120 rpm. After milling, the powder was screened through
an 80 mesh stainless steel screen. The screened powder was hot
pressed in a graphite die at 1750.degree. C. for 80 min at 30.6 MPa
pressure in an argon atmosphere.
As shown in Table II, the properties of the resulting bodies were
compared to a body similarly prepared, but using only 30 v/o
titanium carbide, remainder alumina. As may be seen in Table II,
the bodies prepared as described herein exhibited both modulus of
rupture and toughness which were superior to those of the alumina
tool. The fully dense material exhibited segregation of the metal
phase at triple points in the microstructure.
TABLE II ______________________________________ Modulus of Fracture
Rupture*, Toughness**, Sample Composition MPa MPa.m.sup.1/2
______________________________________ A 38.6 v/o ErAl.sub.11
O.sub.19 + 710 4.5 25.8 v/o Al.sub.2 O.sub.3 + 27.6 v/o (W, Ti)C +
8 v/o (Ni, Al) B Al.sub.2 O.sub.3 + 400 3.5 30 v/o TiC
______________________________________ *Measured by the standard
4Point Bend Test. **Measured by the standard indentation
method.
The present invention provides novel improved materials exhibiting
high thermal stability, high hardness, fracture toughness, and
strength, and high wear resistance and impact resistance. These
materials are suitable for such applications as high temparature
structural materials or as wear resistant materials in applications
such as sand blasting nozzles, pump seals, cutting tools, and the
like.
While there have been shown and described what are at present
considered the preferred embodiments of the invention, it will be
obvious to those skilled in the art that various changes and
modifications can be made therein without departing from the scope
of the invention as defined by the appended Claims.
* * * * *